The present invention pertains to a device for operation of a fluid circuit comprising a principal line and at least a heat exchanger and a cycled control valve for regulation of fluid flow. The fluid circuit is preferably a heating circuit in a vehicle.
It is known to provide in the heating circuit for an automotive vehicle a cycled control valve for regulation of the flow volume of the heating fluid, i.e., for control of the heat output of the heat exchanger. (See, e.g., DE-OS No. 25 31 015 and DE-OS No. 26 15 476) Such a control valve is operated with only two control positions, i.e., either "open" with the cross section of the valve completely open, or "closed" with a completely closed cross sectional area. The changeover from one valve setting to the other takes place in a very short time, so that a strong deceleration of the moving fluid mass occurs. These decelerated fluid masses lead to peaks of overpressure in front of the closed valve, and this has a detrimental effect on the entire fluid circuit and may lead to the destruction of tubing, hoses, connecting pieces, etc. In the direction of the flow behind the closed valve, peaks of low pressure occur, which among other consequences lead to vapor separation and the formation of vapor bubbles in the heating medium, thus effecting a non-uniform contact with the heat exchanger located downstream in the heater device. Furthermore, the flow control of the heating fluid in the case of low and medium heat outputs basically results in an unfavorable temperature distribution in the heat exchanger. The heat exchanger of the heater is heavily supersaturated on the air side, and the average flow velocity of the heating fluid is low. On its way from the inlet of the heat exchanger through the heat exchanger to the outlet of the heat exchanger, the heating fluid is thereby cooled almost entirely at the onset of this path, so that during the remaining portion of the path practically no heat exchange and thus no heating of the air takes place. As a result, strong temperature gradients are also produced in the air flow. Such a layer-like variability of the temperature of the heated air flow is undesirable for a comfortable regulation of the heating, on the one hand, because the passengers in the vehicle are exposed to differently heated air, and on the other, because it is technically not possible to detect the representative air outlet temperature downstream of the heat exchanger with a single sensor, or at least this is possible only at a considerable expense.
Various measures have been proposed to avoid a layered temperature distribution. For example, it is disclosed in DE-OS No. 23 10 709 to insert a bypass line in a heating circuit for a vehicle in combination with a pump, whereby the regulation of the flow of the heating medium in the principal line is effected by means of a continuously variable control valve, and the control of the flow in the bypass line is regulated by means of a suitably dimensioned diaphragm in combination with the pump between the bypass and the heat exchanger. One disadvantage of this proposed measure is that an additional device in the form of a pump to increase the pressure is required to maintain a bypass flow and hence the intermixing of cooled heating medium. Since this heating circuit operates with a continuously regulated volume control valve, the problem of pressure impacts does not arise in the fluid circuit.